A nonwoven fabric may be understood as a textile fabric that is not made by the conventional weaving or knitting process. A nonwoven fabric may be made by first laying down a mat comprising of a plurality of continuous filaments or non-continuous fibers, followed by mechanical, thermal, chemical or combinations thereof to bind the individual filaments or fibers together into the said nonwoven fabric. The fiber commonly used in the nonwoven industry may include polyester, polyolefin, polyamide, polyvinyl alcohol, polyacrylate, cellulosic, rayon, polyurethane, polysulfone, polyphenyl sulfide, etc. Typical fiber lengths may range from 0.05 inches and higher, and more commonly from 0.25 inches to 3 inches, and typical fiber diameters may range from 0.1 micrometers and higher, and more commonly from 5 to 50 micrometers.
Conventional nonwoven manufacturing may consist of taking fibers from tightly packed bales, separating large fiber bundles in a process called bale opening, mixing different fiber types (if two or more fiber types are used), followed by a process of coarse and fine opening and blending, before laying down the fiber mat by commonly used methods such as the dry-laid or air-laid processes. Said common methods for laying down a mat comprising of a plurality of fibers may include (1) dry-laid, where the individual fibers may be separated from one another by combing within a set gap between a pair of toothed plates or rolls then laid down as a fiber mat onto a conveyor, and (2) air-laid, where the individual fibers may be separated from one another and laid down as a fiber mat by means of a controlled air current rather than toothed plates or rolls. Common methods for binding the laid down fiber mat may include (1) mechanical techniques such as stitch-bonding, or needle-punching the fiber mat to effect fiber to fiber entanglement, (2) thermal techniques such as heating the fiber mat to its softening or melting temperature and applying pressure to effect fiber to fiber adhesion, and (3) chemical technique such as adding solvent, adhesive or chemical bonding agent to the fiber mat to effect fiber to fiber adhesion.
Fibers that are made for dry-laid and air-laid methods may typically be crimped, i.e. the individual fibers are not straight but are configured in a zig-zag or loopy fashion, with each fiber containing one or more, and more commonly five to thirty individual crimps, i.e. zig-zags or loops. Such zig-zags or loops may be imparted on individual fibers in a process called crimping, by applying dry heat or steam to heat set the fibers pressed into a zig-zag or loopy configuration in a crimp box to effect the required extent of crimp. Such crimping may be necessary for fibers to grasp onto each other during the laid down process. Fibers without said crimp, i.e. straight fibers, may not possess the necessary frictional or cohesive strength required for the laying down process, resulting in constant and random breakages and rendering it difficult to proceed with the subsequent binding process.